In an internal combustion engine, it is desirable to treat the exhaust gases so that they can be discharged in a relatively safe condition into the atmosphere. In some engines, particularly of the diesel type, among the greatest operating problems is the presence of solid particles which are carried from the engine in the hot exhaust gas stream.
These particles are normally bits of combustible carbon. They result from the incomplete combustion of hydrocarbon fuels under particular engine operating conditions. However, the operating efficiency of the engine is also a contributing factor to the amount of the carbon which will be produced during the combustion event.
The presence of relatively large amounts of carbon particles in any exhaust stream is evidenced by a dark, smoky effluent. Such smoke is not only offensive to the smell; in large quantities it can be unhealthy.
Means have been provided, and are known to the prior art, for the elimination or minimization of the carbon content in any exhaust gas stream. However, it has been found that while the carbon particles can be eliminated by a suitable filter of proper construction, eventually the latter can become saturated and/or inoperable due to excess carbon accumulation.
It should be appreciated that generation of carbon particles in an exhaust gas stream is prevalent under virtually all diesel engine operating conditions. It is further appreciated that the quantity and quality of the exhaust gas stream created in any internal combustion engine will vary in accordance with the operating characteristics of the engine.
For one thing, the temperature range experienced by the diesel exhaust gas stream can vary between slightly lower than ambient temperature, and temperature in excess of 1500.degree. F.
When the gas exits from the engine at such a high temperature, the combustible carbon particles within the stream will generally be ignited and discharged into the atmosphere in gaseous form. This ignition of the carbon particles will continue even though the engine operation temperature drops down to as low as 650.degree. F.
Where, however, it is found that the engine operates continuously under such circumstances that carbon is continuously produced and accumulated in the filter, the latter must be occasionally rejuvenated. Under usual circumstances, rejuvenation will merely consist of introducing the hot exhaust gas stream into the filter itself to contact carbon which has been retained in the latter. This is achieved however, only so long as the gas is above the carbon ignition temperature.
The combustion of any large, and contained carbon accumulation can, and will often produce temperatures beyond that of the exhaust gas. The result is that at such excessive temperatures the filter is susceptible to thermal shock and perhaps even to damage such as being distorted, or weakened in other ways.
Toward overcoming the above noted problems particularly in diesel engine operation, the present invention provides the means for minimizing thermal shock and possible damage. In the instant arrangement, the particle filtering bed is disposed as near as possible to the engine's hot exhaust gas passages. Preferably, the filter is positioned to receive the exhaust gas stream as the latter leaves the engine combustion chambers.
In such a position, the filter will always receive exhaust gas at or near its maximum temperature. Even at initial engine start-up, when the gas is relatively cool and incapable of initiating combustion of the particles, the filter bed will commence being heated to an operating condition.
In a relatively short period of time, usually when the engine begins to operate normally, the filter bed will become sufficiently hot to burn off retained particles. However, such burning is regulated or controlled, by injecting a stream of a gaseous coolant into the bed.
Thereafter, as the engine operates under different known loading conditions, the temperature of exhaust gas will vary between about 400.degree. to 1500.degree. F. With the present arrangement for heating and/or cooling the filter bed, the latter will be maintained in a relatively stable condition and within a desired temperature range.
Thus, during the engine warm-up period or when it is operating under light load conditions and the exhaust gas comes out at a relatively low temperature, the gas stream will be preheated by an electrically actuated heater coil within the filter. This heating step arrangement is periodically brought to function in response to a particular condition of the gas within the filter bed.
Means is further provided for introducing a coolant, such as air, into the filter bed. Thus, the heating and cooling functions can be alternately activated thereby to maintain the bed within a desired temperature range deemed to best preserve the filter's integrity.
By so regulating and stabilizing the temperature of the exhaust gas within the filter bed, the latter is preserved from thermal or physical damage. Further, it is permitted to operate in a most efficient manner by substantially eliminating the presence of carbon in the engine exhaust gas stream.
It is therefore an object of the invention to provide an exhaust gas system which is capable of filter rejuvenation. A further object is to provide a filter rejuvenation means which is capable of continuous operation whereby to avoid a build-up within the filter of combustible particles. A still further object is to provide a system which is capable of adjusting to engine operating conditions whereby to avoid any excess in particle build-up which might eventually result in excessive temperatures within the filter body.